fix #29182, generate top level const fields lazily

pkg/dev_compiler/test/codegen_expected/es6_modules.js

Index: pkg/dev_compiler/test/codegen_expected/es6_modules.js
diff --git a/pkg/dev_compiler/test/codegen_expected/es6_modules.js b/pkg/dev_compiler/test/codegen_expected/es6_modules.js
index 59effa39e3131aece559cfcba0fd5e3aa4cf0fc4..c4cb433d1486875642a940ff288e7cfa0499f643 100644
--- a/pkg/dev_compiler/test/codegen_expected/es6_modules.js
+++ b/pkg/dev_compiler/test/codegen_expected/es6_modules.js
@@ -25,18 +25,23 @@ dart.fn(es6_modules.f, VoidTodynamic());
 es6_modules._f = function() {
 };
 dart.fn(es6_modules._f, VoidTodynamic());
-es6_modules.constant = "abc";
-es6_modules.finalConstant = "abc";
 dart.defineLazy(es6_modules, {
+  get constant() {
+    return "abc";
+  },
+  get finalConstant() {
+    return "abc";
+  },
   get lazy() {
     return dart.fn(() => {
       core.print('lazy');
       return "abc";
     }, VoidToString())();
-  }
-});
-es6_modules.mutable = "abc";
-dart.defineLazy(es6_modules, {
+  },
+  get mutable() {
+    return "abc";
+  },
+  set mutable(_) {},
   get lazyMutable() {
     return dart.fn(() => {
       core.print('lazyMutable');